This invention relates to an optical telecommunications system. More specifically, this invention relates to an optical telecommunications system which uses phase compensation interferometry.
At present, digital and analogue transmission employ a variety of systems for telecommunications including point to point microwave radio, optical fiber cable link, copper cable link, and communication satellite transmission. Such systems are used for transmitting telephone calls, television signals, and other audio and/or visual signals as well as various data telecommunications. In recent years, the trend has been toward the use of increasing numbers of optical fiber links. Such systems generally use optical fiber in a passive role for transmitting data and communications point to point using conventional electronics for all amplification and multiplexing requirements. That is, the optical fiber cable between the transmitter and receiver is essentially a dumb link.
In present systems, information is usually multiplexed in time division format. The diverse signals are multiplexed together by combining them temporally. For example, 24 digital signal zero (DS0) level signals are sampled sequentially and combined to form the next level of signal transmission which is T1 (DS1). The outputs of 4 T1 transmitters may be sampled and stacked sequentially in time by a T2 (DS2) multiplexer. Similarly, the outputs of 28 T1 or 7 T2 transmitters may be sequentially sampled and combined by a T3 (DS3) multiplexer. This process of combining or multiplexing lower level telemetry signals is repeated many times until signals in the Gb/snd range are produced.
The above approach has a number of disadvantages. European protocol differs from U.S. protocol. Thirty-two DSO signals are combined by a E1 multiplexer, the European counterpart of T1. Thirty of the 32 E1 channels transmit DSO signals while the other two channels are used for signaling and alarm/supervision purposes. In general, European and U.S. standard telemetry is not mixed. The byte rates and formats differ. Likewise, while DS3 and synchronous optical network (SONET) formats may be combined in the same transmission facility, the DS3 is limited to non-drop/insert applications. In other words, such arrangements make it difficult to drop out signals and insert signals at intermediate ends of the transmission path. In such cases, at a point further down the facility, a portion of the signals are separated and diverted from the cable, while the remainder plus some additional information inserted at the same location continues to propagate along the cable. However, at such points, the multiplexed signal must be electronically broken down into basic DS3, DS2, DS1, DS0, ATM wideband and fractional wideband data operating at DS3 and SONET rate, sorted, and recombined. This requires significant quantities of electronics including both a digital demultiplexer, one or more multiplexers, and microprocessors as illustrated in the prior art FIG. 1.
U.S. Pat. No. 4,477,723, issued Oct. 16, 1984 to Edward F. Carome and the present inventor, hereby incorporated by reference, discloses a technique of using phase modulation to detect electric fields. An interferometer configuration is used.
The present inventor's prior U.S. Pat. No. 4,755,668, issued Jul. 5, 1988, and hereby incorporated by reference, discloses phase modulation interferometer techniques for use with a plurality of sensors.
The following patents disclose various other phase modulation techniques for use with telecommunications and/or sensors:
______________________________________ Patent No. Inventor ______________________________________ 4,699,513 Brooks et al 4,848,906 Layton 4,860,279 Falk et al 4,866,698 Huggins et al 4,882,775 Coleman 5,191,614 LeCong 5,223,967 Udd ______________________________________
Although the above and other techniques have been generally useful, they have often been subject to one or more disadvantages. For example, the capacity to carry a large number of signals within a single transmission path, such as optical fiber, is often limited. In some techniques, drop/insert operations (picking off a signal and inserting another signal) at an intermediate stage in a transmission path require complex electronics. Some techniques provide questionable security for transmission of telecommunications such as audio, video, and/or data. Some techniques do not readily or easily provide full duplex transmission within a single fiber. Some prior techniques don't readily allow redundant transmissions.